# std::atomic<T>::is_always_lock_free

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< cpp‎ | atomic‎ | atomic

static constexpr bool is_always_lock_free = /*implementation-defined*/; |  | (since C++17)

Equals true if this atomic type is always lock-free and false if it is never or sometimes lock-free.

The value of this constant is consistent with both the macro `ATOMIC_xxx_LOCK_FREE`, where defined, with the member function is_lock_free and non-member function std::atomic_is_lock_free.

### Notes

There is no non-member function equivalent of this static member constant because non-member functions take pointers to atomic types, and therefore aren't as useful in constant expressions.

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_atomic_is_always_lock_free` | `201603L` | (C++17) | `constexpr atomic<T>::is_always_lock_free`

### See also

is_lock_free | checks if the atomic object is lock-free (public member function)
atomic_is_lock_free (C++11) | checks if the atomic type's operations are lock-free (function template)

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